The craniofacial region is particularly susceptible to wounds resulting from automobile, industrial, and athletic accidents and inter-personal violence. These wounds commonly present as large nonunion defects which will not spontaneously repair and ultimately require bone grafts into order to restore bony continuity. Nonunions form fibrous connective tissue and, less frequently, fibrocartilage as part of their reparative process. This project will attempt to define a cellular mechanism for the lack of ossification in large craniofacial defects. A craniofacial nonunion model will be developed in rats using 8 mm craniotomy defects. Tissue harvested from the defects will be examined histologically at time periods from one day to six weeks. Defect tissue will be cultured to examine the cellular subpopulations present. Primary through third passage cultures will be analyzed for optimum plating densities, changes in phenotype, and cell viability. Assays include production of type II collagen (cDNA, SDS-PAGE), non-collagenous proteins, and proteoglycan, and matrix vesicle biogenesis (enrichment of alkaline phosphatase and 5'-nucleotidase v. ouabain sensitive Na+/K+ ATPase compared to cell membranes), 3H-thymidine incorporation and cell number. Time course and dose responses will be assessed. The effect of BMP or DBP on nonunion cells will be compared to the biochemical behavior of authentic chondrocytes, using responsiveness to 1,25(OH)2D3 or 24,25(OH)2D3 as a differentiation marker. Defects in calcification-specific matrix vesicle enzymes and extracellular matrix proteins will be examined using cDNA probes. Expression of nuclear protoncogenes will be measured to determine whether the defect is due to failure to express proteins involved in cytodifferentiation. Such defects at the cellular level may contribute to the lack of ossification in nonunions. Data obtained will improve presently used techniques for bone grafting of craniofacial nonunions.